The present invention generally relates to a photographic camera having an automatic focusing device for automatically moving an objective lens of the camera to one of different focal positions whereat an image of a target object formed on a focal plane in the camera is in proper focus.
There is known an auto-focus camera utilizing a zone-monitoring rangefinder which basically comprises a light emitter for projecting a beam of light to illuminate the target object located within one of zones of distances away from the camera, a light receiver for detecting the beam of light reflected from the target object and including photoresponsive elements so arranged as to monitor the respective zones of distances, each of the photoresponsive elements having a parameter the magnitude of which varies as a function of the intensity of the beam of light detected thereby, and means coupled to the light receiver and responsive to change in magnitude of the parameter of any one of the photoresponsive elements to provide an automatic focus control signal necessary to actuate a trigger mechanism to bring the objective lens to one of the focal positions which corresponds to the distance range from the camera to such one of the zones of distances when the magnitude of one of the photoresponsive elements monitoring such one of the zones of distances has actually varied due to the presence of the target object in such one of the zones.
Examples of the auto-focus camera of the type referred to above are disclosed in the U.S. Pat. No. Re. 27,461 reissued on Aug. 15, 1972, the U.S. Pat. No. 3,723,003 patented on Mar. 27, 1973, and the Japanese Patent Laid-open Publication No. 49-49625 laid open to public inspection on May 14, 1974.
There is also known an auto-focus camera utilizing a zonal rangefinder which basically comprises first and second stationary receiving means for receiving radiation from a target object along first and second spatially separated light paths, respectively, stationary sensing means arranged to provide electrical signals representative of the relative position of the intensity distribution of the radiation passing through the first stationary receiving means with respect to the position of the intensity distribution of the radiation passing through the second stationary receiving means, and circuit means responsive to the electrical signals to provide a focus control signal representative of the distance between the target object and the camera.
The auto-focus camera utilizing the zonal rangefinder of the type referred to above is disclosed in the U.S. Pat. No. 3,945,023 patented on Mar. 16, 1978.
In the auto-focus camera disclosed in any one of the prior art references referred to above, the focus adjustment to bring the camera objective lens to one of the focal positions whereat the image of the target object to be photographed is in proper focus on a focal plane in the camera is substantially completely automated.
On the other hand, when it comes to a manual focus adjustment capability, it appears that the conventional auto-focus camera requires the operator or photographer to adjust the position of the camera objective lens manually in accordance with the estimation of the camera-to-object distance or until the image of the target object appearing in the viewfinder arrangement is sharply focused. In this case, the substantially whole number of electric and/or electronic circuit components necessary to achieve the automatic focus adjustment are generally rendered inoperative. In particular, when the electric and/or electronic circuit components necessary to achieve the automatic focus adjustment are to be rendered inoperative, what is most important is to disengage the trigger mechanism operable to move the camera objective lens to any one of the focal positions, which may be constituted by a pinion and rack arrangement or a pawl and tooth arrangement, so that a drive will not be transmitted from a drive unit, either an electric motor or an electromagnetic device, to the camera objective lens.
However, where the trigger mechanism includes a biasing spring for urging the camera objective lens to either one of the near and hyperfocal positions, the manual focus adjustment capability cannot be appreciated.
On the other hand, even though the trigger mechanism does not include such a biasing spring as described above, the camera must have a conventional device or devices which enable the operator to focus the camera objective lens properly by visually observing the quality or composition of one or more images of the target object to be photographed and/or the estimation of the camera-to-object distance, separately of a device or devices which are required to achieve the automatic focus adjustment. This appears to involve the increased cost of manufacture of the auto-focus camera.